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Page 3 <br /> fractions in both wells are aliphatic chains with 16 to 21 carbons (C16 to C21). The vapor <br /> pressure for the TPH residual remaining in MW-3 and MW-4 was calculated using Table 2 and <br /> Table 3 information. The resulting vapor pressures for petroleum residual in MW-3 and MW-4 <br /> are 0.013 mm Hg and 0.010 mm Hg, respectively. These values were compared to the vapor <br /> pressure of diesel fuel of 0.400 mm Hg. The weathered material remaining in the ground water <br /> has a vapor pressure 40 times lower than fresh diesel fuel. <br /> In conclusion, the vapor pressure of the remaining low levels of weathered petroleum are too low <br /> to pose a threat to human health. Further to the matter, given the reduced volatility and vapor <br /> pressure of this residual, soil gas testing does not appear to be an appropriate or necessary <br /> measure required to be taken to protect current or future usages of the property. <br /> Sincerely yours, <br /> Linda L. Huff, P.E. <br /> President <br /> Enclosure <br /> cc: James Taylor, ContiGroup Companies, Inc. <br /> Central Valley Regional Water Board <br /> Robert Marty,AGE <br /> RACONTGRAN\Stockton\2008 Correspondence\ltr to H Knoll 061108 Rev 7-21-08.doc <br />